Method of manufacturing an article

ABSTRACT

A method of manufacturing an article comprising: (a) performing an additive manufacturing process to firm an article in an initial state, the article comprising mounting features and being supported during the additive manufacturing process by support structures; and (b) performing a second manufacturing process to transform the article into a second state, which second manufacturing process is a subtractive process comprising: (i) mounting, via the mounting features formed during the additive manufacturing process, the article in a holding device of a machine for operating on the article, with the support structures or at least remnants thereof remaining on the article, and (ii) with the article so mounted in the holding device, processing at least one feature on a surface of the article on which the support structures were provided to remove material on the at least one feature provided by the support structures.

This application is a Continuation of Ser. No. 14/399,560, filed Nov. 7,2014, which is a national stage of PCT/GB2013/051210, filed May 10,2013, which claims priority to GB 1210121.8, filed Jun. 7, 2012, GB1210120.0, filed Jun. 7, 2012, EP 12167541.7, filed May 10, 2012, EP12167533.4, filed May 10, 2012, and EP 12167523,5, filed May 10, 2012.The entire contents of the prior applications are hereby incorporated byreference herein in their entirety.

TECHNICAL FIELD

This invention relates to a method for manufacturing an article, forexample an article comprising at least one dental restoration.

BACKGROUND

Rapid manufacturing techniques are becoming more widely used to producea wide variety of parts, in particular, techniques which build partslayer-by-layer are becoming more well known and used in industry tomanufacture custom parts. Selective laser sintering is one such rapidmanufacturing technique whereby products can be built up from powderedmaterial, such as powdered metal, layer-by-layer. For example, a layerof powdered material can be applied to a bed of the laser sinteringmachine and a laser is then controlled so as to sinter or melt selectparts of the powdered material so as to form a first layer of the part.Another layer of powder is then applied on top and the laser is againcontrolled to sinter or melt another layer of the part. This process isrepeated until the whole part is formed. The formed part is then removedfrom the bed of powder. Such techniques are well known and for instancedescribed in EP1021997 and EP1464298.

Compared to more traditional techniques such as milling parts frombillets or blanks, such techniques offer rapid manufacturing, as well asfacilitate manufacturing of complex parts and can help to minimisematerial wastage. As a result it is becoming more desirable tomanufacture parts using such techniques. Indeed, it is known to use sucha technique for forming dental restorations, and in particular dentalframeworks, which arc typically complex bespoke parts.

However, products made by such a technique sometimes need a furtheroperation. in order to alter the surface finish, and/or the precision ofcertain features on the part, which cannot be achieved via the rapidmanufacturing technique alone.

EP1974688 discloses a technique in which a plurality of dentalprostheses are formed by a rapid prototyping method within a frame, withthe frame being held within a finishing machine tool. WO2011/124474discloses a grip fixture and connector structure to grip a semifinishedpart in a finishing machine tool, the semifinished part being formed byselective laser sintering. EP2238941. discloses a drill template formedby rapid prototyping with reference points used to position the drilltemplate in a milling machine for subsequent processing.

WO2012/064257, published after the priority date of the presentapplication, discloses a dental bridge intermediary structure comprisinga superstructure, the superstructure comprising a connection piece, theconnection piece comprising connection means for connecting the dentalbridge intermediary structure to a cutter.

US 2005/0060868 discloses a re-orientable sample ho comprising kinematicmount features.

The present application describes a method of manufacturing, via anadditive manufacturing process, an article which comprises at least one(e.g. a set of) mounting feature(s) and which When subsequently mountedin a holding device of a machine tool control the position of thearticle to a known position and orientation.

SUMMARY

According to a first aspect of the invention, there is provided a methodof manufacturing an article comprising:

-   -   (a) performing an additive manufacturing process to form an        article in an initial state, the article comprising mounting        features and being supported during the additive manufacturing        process by support structures; and    -   (b) performing a second manufacturing process to transform the        article into a second state, which second manufacturing process        is a subtractive process comprising:    -   (i) mounting, via the mounting features formed during the        additive manufacturing process, the article in a holding device        of a machine for operating on the article, with the support        structures or at least remnants thereof remaining on the        article, and    -   (ii) with the article so mounted in (and held by) the holding        device (to define and maintain its location during the second        manufacturing process), processing at least one feature on a        surface of the article on which the support structures were        provided to remove material (i.e. to remove excess material) on        the at least one feature provided by the support structures.

The article may he supported during the additive manufacturing processon a build plate by the support structures, and the method may compriseremoving the article from the build plate before the mounting step (i).

The mounting features of the article may be kinematic mounting featureswhich engage in the mounting step (i) with corresponding kinematicmounting features on the holding device of the machine.

According to a second aspect of the invention, there is provided methodof manufacturing an article comprising:

-   -   (a) performing an additive manufacturing process to form an        article in an initial state, the article comprising mounting        features; and    -   (b) performing a series of two or more second manufacturing        processes, with each second manufacturing process of the series        comprising:    -   (i) mounting, via the mounting features formed during the        additive manufacturing process, the article in a holding device        of a machine for operating on the article during the second        manufacturing process, and    -   (ii) with the article so mounted in (and held by) the holding        device (to define and maintain its location during the second        manufacturing process), processing at least one feature on the        article,

wherein the mounting features of the article are kinematic mountingfeatures which engage in the mounting step (i) with correspondingkinematic mounting features on the holding device of the machine.

The processing step (ii) in at least one of the second manufacturingprocesses of the series may comprise inspecting or machining orpolishing the at least one feature on the article.

In the processing step (ii) the position and orientation of the articlein three linear and three rotational degrees of freedom within themachine operating volume may be constrained, for example may be knownand defined, by virtue of the interaction of the kinematic mountingfeatures of the article with those of the holding device.

In the processing step (ii) the position and orientation of the articlein three linear and three rotational degrees of freedom within themachine operating volume may be constrained, for example may be knownand defined, (A) by placing the article on the holding device for themounting step (i) in a known gross orientation and (B) by virtue of theinteraction of the kinematic mounting features of the article with thoseof the holding device.

The additive manufacturing process may comprise forming the article,including the mounting features, additively from a material according toa computer model of the article, such that data concerning the positionof the at least one feature on the article, relative to the mountingfeatures, is derivable from the computer model, and the location of theat least one feature may be determined in the processing step (ii) usingdata derived from the computer model concerning the position of the atleast one feature relative to the mounting features of the article.

The processing step (ii) may comprise machining the at least one featureof the article.

The article may comprise at least one product and at least one member onwhich the mounting features of the article are provided which issubsequently detached from the at least one product. The at least onemember may comprise a central hub around which the at least one productis arranged.

The article may be supported during the additive manufacturing processby the support structures on a lower surface of the article. Themounting features of the article may be provided on a surface of thearticle free from the support structures.

The article may be formed layer-by-layer by the additive manufacturingprocess. The additive manufacturing process may comprise a laserconsolidation process. The additive manufacturing process may comprise alaser sintering or laser melting process.

The article may be processed from multiple sides. The article may beturned over during the second manufacturing process.

The at least one feature may be provided with excess material which isremoved during the second manufacturing process.

The article may comprise gross orientation features which restrict thegross orientation that the user can place the article on the holdingdevice of the machine.

The gross orientation features may be configured such that they enablethe article to be placed in one orientation only on the holding device.

The gross orientation features may be provided by the mounting features.Or it may be that the gross orientation features are separate to thekinematic mounting features of the article and do not interfere with thecontrol of the position and orientation of the article provided by theengagement of the kinematic mounting features of the article with thoseof the holding device.

The method may comprise placing the article on the holding device forthe mounting step (i) in a known gross orientation.

The method may comprise using the gross orientation features to placethe article on the holding device for the mounting step (i) in the knowngross orientation.

The mounting features may be formed on one side of the article.

The at least one feature may be processed on the article in theprocessing step (ii) without probing the article beforehand to determineits location within the machine operating volume.

The article may be held in the holding device by a clamping member suchas a screw.

The mounting features may form a set of mounting features and thearticle may comprise a plurality of such sets of mounting features.

According to another aspect of the invention there is provided a methodof manufacturing an article comprising: taking an article formed in aninitial state using an additive manufacturing process, the articlecomprising at least one (e.g. a set of) mounting feature(s); performinga second manufacturing process to transform the article into a secondstate, Which comprises mounting, via the at least one (e.g. set of)mounting feature(s), the article in a holding device of a machine foroperating on the article, wherein the position and orientation of thearticle, for example in three linear and three rotational degrees offreedom, within the machine operating volume is constrained by (and forexample is known and defined by) virtue of the interaction of the atleast one (e.g. set of) mounting feature(s) with the holding device, andprocessing at least one feature on the article.

Accordingly, the additive manufacturing process could have been used toform the bulk of the article and the second manufacturing process couldbe used to finish off certain aspects or features of the article. Theprovision of at least one mounting feature(s) which defines the positionof the article within the machine operating volume can obviate the needto probe the article to determine its location prior to operating on thearticle. The at least one mounting feature(s) can ensure that theposition and orientation of the article is known when it is mounted inthe machine. In particular, it can ensure that the lateral position inthree orthogonal degrees of freedom, and the rotational orientationabout three orthogonal rotation axes is constrained in a known way.Accordingly, the at least one mounting feature(s) could be described asbeing a location defining mounting feature. This can mean that theprocessing of the at least one feature on the article can take placestraight away without time consuming position and/or orientationidentification operations which require inspection of the location ofthe article, e.g. without probing the article to find its location.

There can be two main sources of error in the position of the at leastone feature to be processed. One source of error can be the uncertaintyin the position of the at least one feature to be machined relative tothe at least one (e.g. set of) mounting feature(s) (and hence relativeto the holding device of the machine). This error can be dependent onthe accuracy of the additive manufacturing process. Accordingly, sucherrors can vary depending on the accuracy of the additive manufacturingprocess, but typically are known and can be defined with respect to theprocess used. Another source of error can be the position repeatabilityof the article with the holding device of the machine (which can bedictated by the configuration of the at least one (e.g. set of) mountingfeature(s) and corresponding features on the holding device).Preferably, the at least one (e.g. set of) mounting feature(s) areconfigured such that the ratio of i) uncertainty of the position of thepart (e.g. at least one feature to be machined) to ii) the positionrepeatability of the article is not more than 50:1, more preferably notmore than 10:1, especially preferably not more than 5:1, for example notmore than 4:1, for instance not more than 1:2. As will be understood,the uncertainty of the position of the part and the positionrepeatability of the article can be measured as position tolerancediameters.

Accordingly, preferably the method is configured, and for example the atleast one (e.g. set of) mounting feature(s) of the article and theholding device are configured, such that when the article is mounted inthe holding device, the location of the at least one feature to beprocessed within the machine's operating volume is known to within arequired, e.g. predetermined, tolerance, and for example to within aposition tolerance diameter of 100 μm (microns), more preferably towithin a position tolerance diameter of 50 μm (microns).

The at least one (e.g. set of) mounting feature(s) could be configuredsuch that the linear position along all three mutually perpendicularaxes and rotational orientation about those axes within the machineoperating volume is known and defined by virtue of the interaction ofthe at least one (e.g. set of) mounting feature(s) with the holdingdevice.

For example, the at least one (e.g. set of) mounting features) can bekinematic mounting features. As will be understood, and as for instancedescribed in H. J. J. Braddick, “Mechanical Design of LaboratoryApparatus”, Chapman & Hall, London, 1960, pages 11-30, kinematic designinvolves constraining the degrees of freedom of motion of a body orfeature using the minimum number of constraints and in particularinvolves avoiding over constraining. This ensures highly repeatablepositioning of the article with respect to the holding device, and meansthat the article will sit on the holding device in a predictable knownmanner. Accordingly, such kinematic mount features could engage withcorresponding kinematic mount features on the holding device of the tool(e.g. machine tool) for operating on the article.

It has not previously been considered to use kinematic mount features tohold an article for machining due to the high loads experienced duringmachining. There has therefore been a technical prejudice against theuse of kinematic mount features for this purpose.

The article can also comprise gross orientation features which restrictthe gross orientation that the user can place the article on the holdingdevice. In particular, preferably they are configured such that theyenable the article to be placed in one orientation only on the holdingdevice. Such feature could be provided by the at least one (e.g. set of)mounting feature(s). Optionally, they are provided as separate featuresto the at least one (e.g. set of) mounting feature(s). Preferably, suchgross orientation features do not interfere with the control of theposition and orientation of the article provided by the engagement ofthe at least one (e.g. set of) mounting feature(s) on the article andcorresponding features on the holding device.

The article could have been built via the additive manufacturing processaccording to a computer model e.g. a CAD model, of the article.

Accordingly, the second manufacturing process could comprise determiningthe location of features of the article using data concerning theposition of such features. Such data could be derived from the computermodel Accordingly, the method can comprise receiving data concerning theposition of at least some features of the article.

The article could have been built layer-by-layer via the additivemanufacturing process. The article could have been built via a laserconsolidation processes, such as a laser sintering or melting process,also known as selective laser sintering or selective laser melting.Optionally, the article could have been built via a laser claddingprocess, a fused deposition modelling (FDM) process or an e-beam meltingprocess. The method can comprise the step of forming the article via theadditive process.

The second manufacturing process can be a subtractive process.Accordingly, processing the at least one feature can comprise removingmaterial from the article. For example the machine can be a machinetool, and in which the second manufacturing process comprises machining,for example milling, at least a part of the article.

The article could be processed from multiple sides. For instance, thearticle could be processed on opposing sides. This could be achieved bymounting the article such that it can he accessed on multiple sides bythe processing machine. This could be achieved by turning the articleduring the second manufacturing process. Accordingly, the secondmanufacturing process can comprise processing a first side of thearticle and subsequently turning the article so as to perform anoperation on another side of the article. More particularly, the secondmanufacturing process can comprise processing a first side of thearticle and subsequently turning the article over so as to perform anoperation on an opposite side of the article. This could for examplecomprise machining a first side of the article and subsequently turningthe article so as to machine an opposite side of the article. Thearticle could be turned by the holding device. That is the holdingdevice could have an axis of rotation.

It might be that the at least one feature is formed entirely during thesecond manufacturing process. Optionally, the at least one feature canhave already been at least partially formed in the article via theadditive manufacturing process. Accordingly, processing the at least onefeature can comprise finishing the at least one feature. This couldcomprise removing material on the at least one feature. Accordingly, theat least one feature could be provided with excess material which isremoved during the second manufacturing process. Accordingly, when themethod comprises forming the article via the additive processes, thisstep can comprise adding excess material onto at least the at least onefeature, Such excess material can be material in. excess to what isultimately desired for the finished product.

The article can comprise at least one dental restoration. The articlecould comprise at least one implant supported dental restoration. Thedental restoration could be an abutment. The dental restoration could bea single tooth restoration, for example an implant supported abutment ora crown. Other material could be added to the dental restoration tofinish the restoration. For instance, porcelain or a crown could beadded to provide a finish that is more aesthetically similar to naturalteeth.

The second manufacturing process can comprise machining a part of thedental restoration that is to interface with another object, e.g.another member in a patient's mouth. This can be important to ensure agood fit, Ensuring a good fit can be important for many reasons, e.g.structurally so as to reduce the chance of failure of the dentalrestoration. It can also be important to ensure a good fit so as toreduce or avoid gaps which could harbour bacteria. For instance, themethod can comprise machining a region that is to interface with a toothprepared for receiving the restoration, commonly known as a “prep” in apatient's mouth, or an implant in a patient's jaw, The dentalrestoration could comprise at least one portion for interfacing with atleast one member in a patient's mouth, e.g. at least one implant member,and the second manufacturing process comprises machining said at leastone portion.

The article can comprise a plurality of products joined together. Aswill be understood, the products can be subsequently separated from eachother. Accordingly, a plurality of products can be formed and processedconcurrently. As they are joined together, they can be transportedtogether and mounted together in a machine for performing the secondmanufacturing process.

The article can comprise at least one product and at least one member onwhich the at least one (e.g. set of) mounting feature(s) are provided.Accordingly, the at least one (e.g. set of) mounting feature(s) can beprovided separate from the product(s). As will be understood, the atleast one member can be subsequently separated from the productsubsequent to all processing requiring the member. The member could be aholding member (e.g. a clamp member) via which the article can be held(e.g. clamped) to define and maintain its location during the secondmanufacturing process. The at least one member may comprise a centralhub around which the at least one product is arranged.

The plurality of products can be joined together via the at least onemember.

The plurality of products can comprise a plurality of dentalrestorations. For instance, the plurality of products can comprise aplurality of dental abutments.

Where the article was supported during the additive manufacturingprocess by scaffolding on a lower side of the article, the at least onefeature being processed on the article may be on the same side as saidscaffolding.

The at least one feature may be processed on the article during thesecond manufacturing process on a surface of the article on which thescaffolding was provided.

According to another aspect of the invention, there is provided a methodof manufacturing an article comprising: taking an article in an initialstate formed using an additive manufacturing process, the articlecomprising at least one mounting feature; and performing a secondmanufacturing process to transform the article into a second state,which comprises mounting, via the at least one mounting feature, thearticle in a holding device of a machine for operating on the article,and processing at least one feature on the article; wherein the articlewas supported during the additive manufacturing process by scaffoldingon a lower side of the article, and wherein the at least one feature isprocessed on the article during the second manufacturing process on thesame side as said scaffolding.

The position and orientation of the article in three linear and threerotational degrees of freedom within the machine operating volume may beknown and defined by virtue of the interaction of the at least onemounting feature with the holding device.

The at least one mounting feature may comprise kinematic mount featureswhich engage with corresponding kinematic mount features on the holdingdevice of the machine tool.

The at least one feature may be processed on the article during thesecond manufacturing process on a surface of the article on which thescaffolding was provided.

According to another aspect of the invention, there is provided a methodof manufacturing a dental restoration comprising: i) forming a dentalrestoration. body in an initial state via an additive process, thedental restoration body comprising a mount having at least one set oflocation features; ii) mounting the dental restoration body in itsinitial state into a machine tool via the mount's at least one set oflocation features; and iii) machining the dental restoration body fromboth substantially opposing first and second sides of the dentalrestoration body to transform the dental restoration body into asecondary state.

Accordingly, the method of the invention utilises differentmanufacturing techniques at different stages to form an accurate dentalrestoration in an efficient manner.

The use of an additive process can be advantageous over machining theentire dental restoration body from a solid blank as it requiressignificantly less material and also can be less time consuming. It alsoallows the formation of a geometry that would be impossible withmachining processes alone.

The provision of the location features can remove the need for probingto ascertain the dental restoration body's position within the machinetool. The location features can ensure that the location of the dentalrestoration body is known when it is mounted in the machine tool.

Step iii) can comprise machining the dental restoration body from thefirst side of the dental restoration body, re-orienting the initialstate dental restoration, and then machining the dental restoration bodyfrom the second side of the initial state dental restoration body.

The at least one set of location features can comprise at least one setof kinematic mounting features.

The dental restoration body can comprise at least one interface forinterfacing with an implant in a patient's jaw (so as to locate thedental restoration in the patent's jaw) which is presented on one ofsaid first and second sides of the dental restoration.

It can be important that the at least one interface (the area(s) of thedental restoration body which mate with the implant(s) in the patient'sjaw) has a very precise finish. Without such a precise finish, the fitbetween the implant(s) and interface(s) could be inadequate and whichcan lead to the dental restoration being inadequately secured within thepatient's jaw.

Accordingly, in the dental restoration body's initial state, the atleast one interface can be formed with an excess of required material.The method can further comprise machining said at least one interface toremove at least some of said excess material.

A plurality of interfaces, spaced along the dental restoration body canbe provided. This is especially the case when the dental restoration isan implant bridge. It has been found that if the plurality of interfacesare not accurately formed, for example if the spacing between theinterfaces differs from the spacing between the corresponding implantsin the patient's jaw, then the dental restoration body can becomecontorted when fixed into position. This contortion can leads tostresses in the dental restoration body, which in turn can lead toundesired stresses on the implants. Such stress on the mounts can causediscomfort for the wearer and a tendency for the dental restoration bodyto work itself loose, or even fail.

Accordingly, the method can comprise machining at least one of saidplurality of interfaces so as to remove excess material, therebymanipulating the relative position of said plurality of interfacesrelative to each other.

The at least one interface can be provided on the second side of thedental restoration body.

The at least one interface can be an implant interface for interfacingwith an implant secured into a patient's jaw.

The dental restoration body in its initial state can comprise at leastone bore for receiving a fastener for securing the dental restorationbody to an implant in a patient's jaw. As will be understood, thesurface against which the head of a fastener abuts the dentalrestoration body against can require a high level of smoothness in orderto ensure a secure fit. The method can therefore comprise machining saidat least one bore so as to provide a final formation of said at leastone bore.

The machining of said. at least one bore can be performed from saidfirst side of the dental restoration body.

An additive process can comprise a selective laser melting/sintiringprocess.

The dental restoration can be an abutment. The dental restoration can bean implant supported abutment.

The dental restoration body can form the final outer shape of the dentalrestoration. Optionally, the dental restoration body can be a body, or“framework”, onto which an outer structure can be formed to provide thefinal outer shape of the dental restoration, Accordingly, the method cancomprise adding an outer structure onto the body. The outer structurecan comprise a layer of porcelain.

According to another aspect of the invention, there is provided a methodof manufacturing an article comprising: forming an article in an initialstate using an additive manufacturing process, the article comprising atleast one (e.g. set of) mounting feature(s), e.g. at least one set ofkinematic mount features (i.e. formed via the additive manufacturingprocess). The method can comprise mounting the article in a holdingdevice of a machine via the set of kinematic mount features.

According to a further aspect of the invention, there is provided anarticle made by an additive manufacturing process comprising at leastone (e.g. set of) mounting feature(s), e.g. at least one set ofkinematic mount features.

According to a further aspect of the invention, there is provided anarticle made by an additive manufacturing process comprising at leastone feature requiring processing in a second manufacturing process,wherein the article was supported. during the additive manufacturingprocess by scaffolding on a lower side of the article, and wherein theat least one feature to he processed during the second manufacturingprocess is on the same side as said scaffolding. The scaffolding, or atleast remnants thereof, may remain on the article.

The article may comprise at least one dental restoration.

The at least one feature may comprise at least one portion of the dentalrestoration that is to interface with another member in a patient'smouth. The second manufacturing process may be one in which said atleast one portion is machined.

The at least one feature may comprise at least one portion forinterfacing with at least one implant member.

According to a further aspect of the invention, there is provided amethod of manufacturing an article comprising: taking an article in aninitial state, the article comprising at least one mounting feature; andperforming a series of two or more manufacturing processes to transformthe article into a different respective state in each manufacturingprocess of the series, comprising, for each manufacturing process of theseries: mounting, via the at least one mounting feature, the article ina holding device of a machine for operating on the article during thatmanufacturing process, wherein. the position and orientation of thearticle in three linear and three rotational degrees of freedom withinthe machine operating volume is known and defined by virtue of theinteraction of the at least one mounting feature with the holdingdevice, and processing the article.

The at least one mounting feature may comprise kinematic mount featureswhich engage with corresponding kinematic mount features on the holdingdevice of the machine.

The article in the initial state, with the at least one mountingfeature, may be formed using an additive manufacturing process.

According to a further aspect of the invention, there is provided aproduct or article produced by a method as described herein,

This application also describes a method of manufacturing a dentalimplant-supported abutment comprising: building an abutment, includingthe part for interfacing with an implant member, from a powderedmaterial, layer-by-layer, via a laser sintering process. Such a methodcan comprise processing at least a part of the abutment subsequent tosaid laser sintering process.

Said processing can comprise removing material from the abutment, e.g.via machining, The method can comprise processing the part forinterfacing with an implant member. Processing can comprise, subsequentto said laser sintering process, mounting the abutment in a device forholding the abutment during said processing. The laser sintering processcan comprise building a mount connected to the abutment via which theabutment is mounted in the device for holding the abutment during saidprocessing. Preferably, the abutment and mount are configured such thatwhen the abutment is mounted in the device for holding the abutmentduring said processing, the abutment's longitudinal axis, which couldfor example be parallel or even coincident with the axis of any currentor yet to be formed bore of the abutment (through which an implantscrew, or screwdriver for fastening an implant screw can be received),and optionally for example the axis of the part for interfacing with theimplant member, is parallel to the tool, e.g. cutting tool, forprocessing the abutment. The laser sintering process can comprisebuilding a plurality of abutments connected to the same mount. At leasttwo, and preferably all, of the plurality of abutments can be orientedsuch that their part for interfacing with an implant member are orientedin the same direction, e.g. such that their longitudinal axes areparallel to each other.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows schematically a selective laser sintering machine forforming an article;

FIG. 2 shows schematically a cross-sectional view of an implant abutmentattached to a supporting implant;

FIGS. 3 a and 3 b show schematically underside views of an articlecomprising a plurality of abutments connected to a central hub in itsinitial state;

FIGS. 4 a and 4 b show schematically top-side views of the article shownin FIG. 3 ;

FIG. 5 is a flowchart illustrating a method according to the invention;

FIG. 6 shows schematically a cross-sectional side view of the lasersintered article of FIGS. 3 and 4 still attached to a build plate duringmanufacture;

FIG. 7 shows a schematic cross-sectional side view of the laser sinteredarticle of FIGS. 3 and 4 damped using a kinematic mount in a machinetool; and

FIG. 8 a shows schematically the implant interfaces being machined intothe underside of a dental restoration and FIG. 8 b shows schematicallythe article turned upside down by the clamp member in preparation forcounter bores to be machined into the abutments.

DETAILED DESCRIPTION

The below description provides an example of how the invention can beused to manufacture an implant-supported abutment. As will beunderstood, an implant-supported abutment is a particular type of dentalrestoration which in use is secured to a dental implant alreadyimplanted into a patient's jaw so as to retain the dental restoration inthe patient's mouth. Typically, an implant-supported abutment is used toreplace a single tooth. Implant-supported abutments are typically madefrom a base structure of metal, with porcelain, a bridge or a crownbeing added to the abutment before it is fitted to provide the desiredfinish form and look of the abutment.

As will be understood, the invention is not limited to the manufactureof implant-supported abutments, but could also be used for instance inthe manufacture of other types of dental restorations, such as bridgesor crowns. However, the invention is also not limited to dentalrestorations in general. Rather, the invention can be used in themanufacture of a wide range of different types of products, such asother types of medical implants, aerospace parts and jewelry.

As will be understood, an implant supported abutment needs to be madeaccurately so as to ensure that the abutment provides a comfortable andenduring fit in a patient's mouth. It is known to use a machine tool,such as a CNC milling machine to produce a dental abutment from a blankor “billet” of sufficient volume so that the entire abutment can bemachined in one piece. As will be understood, for implant-supportedabutments, the blank can be a solid piece of metal, for example titaniumor a cobalt chrome alloy, Other materials can be used, for instancezirconia, although in this case, a metal link member is sometimesrequired between the zirconia body and implant. In any case, such amilling/machining technique results in a highly accurate abutment beingformed, but is time consuming, expensive and involves significantmaterial wastage

The embodiment described according to the present invention makes use ofan additive process to produce an initial form of the abutment. Anadditional machining process is then used to further process at least aselect region of the abutment. The use of an additive process can beadvantageous over machining the entire dental restoration body from asolid blank as it requires significantly less material and also can beless time consuming.

FIG. 1 illustrates a typical arrangement of a build chamber 210 of aselective laser sintering/melting machine. The build chamber 210 definesa space 220 above a lowerable build platform 230. The build chamber 210comprises a powder dispensing and coating apparatus 240 for spreadingpowder 250 over the surface of the build platform 230. A window 255 inan upper wall of the chamber 210 allows a laser beam 260 to be directedto irradiate powder spread at a build surface 270, so as to selectivelysinter/melt the powder thereby forming a layer of the article 20 to bemanufactured, The laser and lowerable platform 230 can be controlled bya controller, 280, such as a PC, which has a program defining theprocess for forming the article 20. The program can control the lasersintering process on the basis of CAD data of the part to be formed. Inparticular, the CAD data can be split into a number of layers, eachlayer corresponding to a layer to be formed by the laser sinteringprocess.

FIG. 2 illustrates how a completed dental restoration, in this case animplant abutment 12, in its final state may be affixed to an implant 4in a patient's jaw bone 5. Neighbouring teeth are not shown in thisdrawing for sake of simplicity, As shown, an outer layer of porcelain 3is added. to the abutment 12 to provide the final outer shape of thedental restoration 2. FIG. 2 shows the implant/abutment interface 6,which is the region at which the abutment 12 and the implant 4 engageeach other, This is a portion of the abutment's 12 surface that is to befinished to a high degree of accuracy. As shown, the abutment 12comprises a counter bore 8 formed in it into which an implant screw 10can be located. The counter bore 8 comprises an upper section 13 andlower section 15. The lower section 15 has a smaller radius than theupper section 13, and in particular has a radius smaller than the headof the screw 10 which is used. to secure the abutment 12 to the implant4. As shown, when screwed into the implant 4 through the counter bore 8,the screw 10 securely fastens the counter bore 8. and hence the abutment12, to the implant 4.

Also shown in FIG. 2 is the emergence profile region 7 between i) theimplant interface 6 and ii) the portion 9 of the abutment 12 onto whichthe porcelain/crown is added (often referred to as the coronal region9). This emergence profile region can also be described as being theregion between the implant interface 6 and the abutment's margin line16. As will be understood the margin line is commonly understood asbeing the edge around the abutment up to which the porcelain or crown isintended to be provided. This region of the abutment's metal surface istherefore exposed and in direct contact with the patient's gums 11, orgingiva, This region is commonly referred to in the dental field as the“emergence profile”, or the “transgingival region”. It can be importantthat this emergence profile region 7 is smooth so as to avoid irritationor the gingiva and also to prevent the harbouring of bacteria. This areacan be smoothed via appropriate polishing techniques,

FIGS. 3 a and 3 b , and FIGS. 4 a and 4 b respectively show undersideand top-side views of an article 20 made from powdered cobalt-chrome viaa laser sintering process Which comprises a plurality of individualabutments 12 each of which is attached to a common location hub 22 via aconnecting bar 21. As shown, the lowermost surface of each abutment 12comprises a. circular disk/boss-like protrusion of excess material 14from which the abutment's 12 implant interface 6 is still to be formedvia machining. The figures also show that on one side of the locationhub 22, there are provided three v-groove features 18 defining akinematic mount. As described below, the three v-groove features 18 areused to accurately locate the article 20 in a known position andorientation in the machine tool apparatus′ volume via the machine toolclamp 25 (described in more detail below). As also shown, the locationhub 22 also comprise two gross-orientation bores 17 extending all theway though the location hub 22. As described below, these bores 17 canbe used to ensure the correct gross orientation of the article 20 in themachine tool clamp 25. As shown, all of the abutments 12 are orientedsuch that their longitudinal axes 32 are parallel to each other.Furthermore (and as illustrated in FIG. 8 a ) the abutment and mount areconfigured such that when the article 20 is mounted in the clamp 25during subsequent processing, the abutment's longitudinal axis 32, isparallel to the cutting tool's 31 longitudinal axis.

FIG. 5 is a flowchart illustrating the method of producing animplant-supported abutment 12 according to one embodiment of theinvention. Each of the steps illustrated will be explained withreference to FIGS. 6 to 8 .

In the first step 110, the abutment 12 in its initial state is producedusing a rapid manufacturing process, which in this example is aselective laser sintering process. As will be understood, the selectivelaser sintering process comprises using a selective laser sinteringmachine such as that schematically shown in FIG. 1 and described above,to repeatedly add layers of powdered. material to the article 20. A highintensity laser is focused on the region of the powdered materialcorresponding to the appropriate shape of the article 20 for theappropriate layer, so as to bind the powder. Subsequently, the surfaceon which the sintering takes place is lowered, so that when the powderedmaterial is next applied the laser may focus at the same height, butscanned around an appropriate course across the powder. In theembodiment described, the abutment 12 is formed as part of an article 20that comprises a plurality of abutments 12 (in this example eightabutments) which are connected to a hub 22 also formed by the lasersintering process.

FIG. 6 shows a cross-section view of an article 20 having beenconstructed by selective laser sintering, but still located on a buildplate 24. The article 20 is resting on a support structure 23, which isa web of sintered material of lesser density than the article, but is ofsufficient strength to support the article and to prevent bothdistortion under its own weight and internal thermal stresses; thesupport structure 23 is also referred to herein as scaffolding or asupport web. As will be understood, although not shown, the build plate24 may be considerably larger than the article 20 being produced and assuch may permit several articles to be built simultaneously. It can alsobe seen from FIG. 6 that, where the article 20 is supported during theadditive manufacturing process by scaffolding 23 on a lower side of thearticle 20, the mounting feature(s) 18 is/are provided on a differentside of the article 20, free from the scaffolding 23 (i.e. on an upperside of the article 20).

The second step 120 follows the completion of the selective lasersintering process, and comprises removing the build plate 24 and thearticle 20 from the selective laser sintering apparatus and preparingthem for machining. Preparation can include various optional stages suchas placing the article 20, along with support web 23 and build plate 24into an industrial oven, in order that a stress relief heat treatmentcycle may be conducted. The article 20 is then removed from the buildplate 24 by cutting the support structures 23, with any remaining partsof the structure 23 removed by pliers and abrasive rotary tools. Thearticle 20 can then be grit blasted to make the entire surface smoother.Even after grit blasting, the side of the article 20 that was connectedto the support structure 23 can sometimes (depending for example on theuse of abrasive tools before blasting) still be significantly rougherthan the opposite side, due to remnants of the support structure 23remaining on the article 20, As shown, the abutments' 12 emergenceprofile regions 7 and the excess material 14 from which the implantinterfaces are to be machined are found on the surface of the article 20on which the support structure 23 was provided.

As previously stated, the machining of the abutments 12 in its initialstate can be a multiple stage process, as the abutment 12 can requirefeatures to be machined from inverse orientations.

As illustrated by FIG. 7 , the following step 130 comprises mounting thearticle 20 in its initial state onto a mounting structure, in this caseclamp 25, in the machine tool, for example a computer numericallycontrolled (CNC) milling machine. FIG. 7 shows schematically a view ofthe article 20 in its initial state clamped into position by the clamp25 engaging the location hub 22. The clamp 25 comprises a base 27 havingthree hemispherical protrusions 28 (only two of which are shown in FIG.7 ) located on its upper surface 30. The protrusions 28 are arrangedsuch that they can engage with the kinematic features 18 on the locationhub 22, thereby facilitating kinematic mounting of the article 20 ontothe clamp 25. The clamp 25 also comprises an upper clamping member 26which engages the location hub 22 so as to urge the location hub 22 intothe base 27, thereby securely holding the article 20 in place. In thiscase, the upper clamping member is a screw 26 that extends through ahole 29 in the location hub 22 so that its screw thread (not shown)engages with a cooperating screw thread in the base member 27, and suchthat as it is tightened, the head of the screw 26 pushes the kinematicfeatures 18 of the location hub 22 into kinematic features 28 of thebase 27. The article 20 is clamped such that the surface to be machinedis facing upwards.

Then at step 140, and as illustrated by FIG. 8 a , the excess material14 provided on each abutment 12 is machined by a milling tool 31 of acomputer numerically controlled (CNC) machine tool apparatus so as toform an implant interface structure 6 which can engage withcorresponding features on an implant 4. The kinematic features constrainthe position and orientation of article 20 and hence the abutments 12within the machine tool's operating volume in all three linear and allthree rotational degrees of freedom. Accordingly, this machining stepcan take place without the requirement to probe the article 20 todetermine its location. That is, the position of the abutments 12 can beassumed from knowledge of where they should be with respect to thelocation hub 22, In the present example, each article 20 is madeaccording to a standard model such that each excess material portion 14can be assumed to be in a predefined position. That is, it is known thatthe article 20 will comprise eight abutments 12 and that the excessmaterial portion 14 of each abutment 12 will be in a predefined locationwith respect to the location hub 22. In particular, in this embodimentthe method, and in particular the kinematic features, are configuredsuch that the position of the abutments 12, and more particularly theposition of the excess material portions 14, are known within a positiontolerance diameter of 100 μm (microns). Accordingly, the accuracy of thelaser sintering process is such that the uncertainty of the position ofeach abutment 12 relative to the kinematic mounting features 18 iswithin a position tolerance diameter of 80 μm (microns) and the positionrepeatability of the assembly is within a position tolerance diameter of8 μm (microns). Hence the ratio of i) the uncertainty of the position ofeach abutment 12 relative to the kinematic mounting features to ii) therepeatability of the kinematic mount features is 10:1.

As the location of the location hub 22 is accurately defined by thekinematic mounting features 18 and 28 on the hub 22 and base 27, theposition of the excess material portions is also accurately defined andknown and can be assumed by the machine tool apparatus performing themilling operation. As will be understood, this need not necessarily bethe case and for instance the location of certain features, such as theexcess material portions 14, can be determined from data. indicating theposition of the features, for instance as determined from, for example,a CAD model of the article used to produce the article during the lasersintering step.

In the embodiment described, the clamp's base 27 is connected to arotation unit 33 which enables the clamp 25 to be rotated about arotational axis A, such that the article 20 can be turned upside down inthe machine tool apparatus. A calibration routine has already beenperformed such that it is known how rotation of the clamp 25 about theaxis A affects the position of the article 20. Accordingly, the nextstep 150 involves turning the article 20 over as illustrated by FIG. 8 band then machining the counter bores 8 so as to finish them to ensure anintimate contact between screw head's shoulder and the mating surface inthe counter bore 8. As the clamp 25 has already been calibrated, it ispossible to accurately finish/form the bores 8 with respect to theimplant interface structures 6. This is important in order to ensurealignment of the counter bores with the implant so as to avoid excessbending forces on the screw connecting the abutment to the implants. inthe described embodiment, the counter bores 8 are partly formed duringthe additive manufacturing process and then precision finished duringthis machining step. However, as will be understood, this need notnecessarily be the case and for example the counter bores could beentirely formed via this machining step (i.e. no counter bore structureis initially formed via the additive manufacturing step at all).

The final step 160 comprises removing the article 20 from the machinetool. The location hub 22 and connectors 21 are detached from theabutments 12, and any remains of the connectors 21 are manually grounddown. A layer of porcelain 3, or a crown structure, can then he added tothe abutments 12 to form the implant abutment before it is secured tothe implant 4 in the patient's jaw.

An embodiment of the present invention is particularly useful formulti-stage processing of an article 20, where the article 20 isrequired to be processed in multiple different machines at differentrespective times, and is required to be held within each machine suchthat the position of parts of the article 20 are known. The provision ofat least one mounting feature on the article 20 which defines theposition of the article 20 within the machine operating volume (withinthe respective operating volume of each different machine in themulti-stage processing) can obviate the need to probe the article 20 ateach stage to determine its location prior to operating on the article20. The at least one mounting feature can ensure that the position andorientation of the article 20 is known when it is mounted in eachmachine of the multi-stage processing. It will be appreciated that sucha benefit can be achieved regardless of how the at least one mountingfeature is firmed, i.e. it need not be by way of an additivemanufacturing process but could for example be formed by a subtractiveprocess such as milling or a combination of these. For example, thedifferent processing stages could include an inspection stage, one ormore machining stages, and a polishing stage, and one or more furthermachining stages. For an example of a polishing stage, see WO2013/167905, Although in WO 2013/167905 the article is not required tobe held in a precise position and orientation within theelectropolishing machine, and is not therefore provided with alocation-defining mounting feature, it will readily be appreciated thatthe electropolishing machine of WO 2013/167905 can be easily adapted toreceive an article having such a location-defining mounting feature. WO2013/167905 also discloses a machining stage following theelectropolishing stage, in which the article is clamped into a machinetool and in which machining operations are performed on the article, forexample machining/milling of abutments.

Referring again to FIG. 6 , it is noted again that the excess material14 from which the implant interfaces are to be machined are found on thesurface of the article 20 on which the support structure 23 wasprovided, i.e. on the same side as the support structure 23. This issomewhat counter-intuitive, because normally one would arrange thearticle 20 during the additive build process in such a way as to placethe support structure 23 away from those surfaces that are considered tobe critical, and to place them on surfaces that do not require a smoothor accurate finish.

For example, for dental frameworks, the critical parts are the implantinterfaces, and the upper surface of the framework is less criticalbecause that will anyway be covered by a layer of porcelain; it is theporcelain that will give the dental restoration its final appearance. Infact, any surface roughness caused by remnants of the support structure23 remaining on the article 20 could be considered as advantageous, foracting as a key for holding the porcelain layer securely.

However, the present applicant has appreciated that there aresignificant benefits in some applications of doing the opposite of whatis considered to be normal, that is to arrange the support structure 23on the same side as the critical interfaces, or any other feature thatis being processed in the second manufacturing stage. In a two-stagemanufacturing process in which the critical interfaces are beingmachined anyway in the second stage, the presence of the supportstructure on the critical interfaces is not an issue. Performing theadditive manufacturing in this orientation also means that there is nomanual finishing or grinding required on the top surface (for example ofan implant bridge); in this respect it is often required to attach apre-made article to this top surface and if it had supports on thesurface, which are ground away, it is unlikely that the surface willhave retained sufficient accuracy for this.

It will be appreciated that, to achieve that benefit, it is notnecessary that the mounting features 18 are of a type (such askinematic) to define the position and orientation of the articleprecisely within the machine operating volume by virtue of theinteraction of the mounting features 18 with the holding device.Therefore, the at least one mounting feature may comprise kinematicmount features which engage with corresponding kinematic mount featureson the holding device of the machine tool, but this is not essential. Ifsuch preformed initial kinematic mount features 18 are not provided, andif the location of the features being processed on the article 20 isimportant (as it is in this case), then an alternative process (e.g. aprobing operation) could be used to determine the location of thearticle 20 within the machine tool's operating volume.

The invention claimed is:
 1. A method of manufacturing an article, themethod comprising: (a) performing an additive manufacturing process toform an article in an initial state, the article comprising kinematicmount features and being supported during the additive manufacturingprocess by support structures, the additive manufacturing processcomprising forming the article, including the kinematic mount features,additively from a material according to a computer model of the article,such that a position of the support structures on the article, relativeto the kinematic mount features, is derivable from the computer model;and (b) performing a second manufacturing process to transform thearticle into a second state, the second manufacturing processcomprising: (i) mounting, via the kinematic mount features formed duringthe additive manufacturing process, the article in a holding device of amachine for operating on the article, with the support structures or atleast remnants thereof remaining on the article, the position andorientation of the article in three linear and three rotational degreesof freedom within the machine operating volume being known and definedby the interaction of the kinematic mount features with the holdingdevice, and (ii) with the article so mounted, processing the supportstructures on the article to remove material from the support structuresusing knowledge derived from the computer model of the position of thesupport structures on the article relative to the kinematic mountfeatures.
 2. A method as claimed in claim 1, wherein the article issupported during the additive manufacturing process on a build plate bythe support structures, and wherein the method comprises removing thearticle from the build plate before the mounting step (i).
 3. A methodas claimed in claim 1, wherein the location of the support structures isdetermined in the processing step (ii) using data derived from thecomputer model concerning the position of the at least one featurerelative to the kinematic mount features of the article.
 4. A method asclaimed in claim 1, wherein the processing step (ii) comprises machiningthe support structures of the article.
 5. A method as claimed in claim1, wherein the article comprises at least one product and at least onemember on which the kinematic mount features of the article are providedwhich is subsequently detached from the at least one product, and the atleast one member comprises a central hub around which the at least oneproduct is arranged.
 6. A method as claimed in claim 1, wherein at leastone of (i) the article is supported during the additive manufacturingprocess by the support structures on a lower surface of the article and(ii) the kinematic mount features of the article are provided on asurface of the article free from the support structures.
 7. A method asclaimed in claim 1, wherein at least one of (i) the article is formedlayer-by-layer by the additive manufacturing process, (ii) the additivemanufacturing process comprises a laser consolidation process, and (iii)the additive manufacturing process comprises a laser sintering or lasermelting process.
 8. A method as claimed in claim 1, wherein the articleis processed from multiple sides, and the article is turned over duringthe second manufacturing process.
 9. A method as claimed in claim 1,wherein the kinematic mount features are formed on one side of thearticle.
 10. A method as claimed in claim 1, wherein the supportstructures are processed on the article in the processing step (ii)without probing the article beforehand to determine its location withinthe machine operating volume.
 11. A method as claimed in claim 1,wherein the article is held in the holding device by a clamping member.12. A method as claimed in claim 1, wherein the kinematic features forma set of kinematic mount features and the article comprises a pluralityof such sets of kinematic mount features.
 13. A method as claimed inclaim 1, wherein the second manufacturing process further comprisesderiving a position of the article relative to the holding device basedon constraints of the kinematic mount features, and the kinematicfeatures are configured such that the derived position is within aposition tolerance diameter of 100 μm or less.
 14. A method as claimedin claim 1, comprising placing the article on the holding device for themounting step (i) in a known gross orientation.
 15. A method as claimedin claim 14, wherein the article comprises gross orientation featureswhich restrict the gross orientation that a user can place the articleon the holding device of the machine, and the gross orientation featuresare configured to place the article on the holding device for themounting step (i) in the known gross orientation.
 16. A method asclaimed in claim 1, wherein the article comprises gross orientationfeatures which restrict the gross orientation that a user can place thearticle on the holding device of the machine.
 17. A method as claimed inclaim 16, wherein the gross orientation features are configured suchthat they enable the article to be placed in one orientation only on theholding device.
 18. A method as claimed in claim 16, wherein the grossorientation features are provided by the kinematic mount features.
 19. Amethod as claimed in claim 16, wherein the gross orientation featuresare separate to the kinematic mount features of the article and do notinterfere with the control of the position and orientation of thearticle provided by the engagement of the kinematic mount features ofthe article with those of the holding device.
 20. A method ofmanufacturing an article, the method comprising: (a) performing anadditive manufacturing process to form an article in an initial state,the article comprising kinematic mount features, the additivemanufacturing process comprising forming the article, including thekinematic mount features, additively from a material according to acomputer model of the article, such that the position of at least onefeature on the article, relative to the kinematic mount features, isderivable from the computer model; and (b) performing a series of two ormore second manufacturing processes, with each second manufacturingprocess of the series comprising: (i) mounting, via the kinematic mountfeatures formed during the additive manufacturing process, the articlein a holding device of a machine for operating on the article during thesecond mnufacturing process, the position and orientation of the articlein three linear and three rotational degrees of freedom within themachine operating volume being known and defined by the interaction ofthe kinematic mount features with the holding device, and (ii) with thearticle so mounted, processing the at least one feature on the articleusing knowledge derived from the computer model of the position of thesupport structures on the article relative to the kinematic mountfeatures.
 21. A method as claimed in claim 20, wherein the processingstep (ii) in at least one of the second manufacturing processes of theseries comprises inspecting or machining or polishing the at least onefeature on the article.
 22. A method as claimed in claim 20, wherein inthe processing step (ii) the position and orientation of the article inthree linear and three rotational degrees of freedom within the machineoperating volume is constrained by virtue of the interaction of thekinematic mount features of the article with those of the holdingdevice.
 23. A method as claimed in claim 22, wherein in the processingstep (ii) the position and orientation of the article in three linearand three rotational degrees of freedom within the machine operatingvolume is constrained (A) by placing the article on the holding devicefor the mounting step (i) in a known gross orientation and (B) by virtueof the interaction of the kinematic mount features of the article withthose of the holding device.